1. Field of the Invention
This invention relates to a coupler between the rotary engine output shaft of a cutter, such as a brush cutter, and a rotary cutting member such as a blade, as well as a cutter equipped with such a coupler.
2. Description of the Related Art
Cutters, such as portable rotary cutters, especially brush cutters, are especially dangerous when they are equipped with a rigid cutting member, such as a blade, disk, or the like. Actually, when the torque transmitted by the engine element of said brush cutter to the cutting member becomes less than the resistant torque applied to the cutting member, in particular when it encounters an obstacle such as a rock, a violent reaction of the entire brush cutter is immediately produced. If the operator is not paying attention, this reaction can injure him. This reaction can be manifested by uncontrolled and sudden movements of the brush cutter, by breaking of the cutting member, or by breaking of all or some of the components of the engine that are unable to react to sudden stoppage of rotation of the cutting element.
To solve this problem, incorporating a torque limiter between the engine shaft and the cutting member has been suggested. For a long time, these torque limiters had been designed based on spring-loaded balls, these balls coming into compressive contact against a suitable race. In such devices, the observed drawbacks include rapid wear of the balls, damage to the race and, overall, poor service life of the torque limiter. Moreover, it turns out that torque control is difficult. Finally, poor heat dissipation is noted.
Other torque limiters using the action of two springs are known. This is the case of patents FR 1222861 and U.S. Pat. No. 3,810,533 that both describe a torque limiting device adapted to a machine comprising a rotor, driven into rotation by an engine, and a cutting device, driven by a stator, this limiting device making it possible to limit the torque transmitted to the stator at high rpm of the rotor. In these documents, the stator is driven by friction pads mounted integrally with the rotor; this entails said pads being constantly subjected to the centrifugal force induced by rotation of the rotor. Thus, when the stator stops suddenly, when the cutting device encounters an obstacle, for example, the pads continue to be applied to the stator with a very high contact pressure at the risk of continuing the driving of the stator. In this device, the centrifugal force is not cancelled when the stator stops, and major heating or damage to the machine in which such a device is installed may result.
More recently, in particular in French Patent Application FR-A-2 829 902, a coupler was proposed with a design that makes it possible to improve the dissipation of heat and to eliminate shock in the operation of the coupler, in particular by obtaining the torque to be transmitted by the radial force between the stator and rotor. In this coupler, the stator bears the pads made in the form of spring-loaded pivoting pins to be applied to the friction lining that is arranged at the rotor level. Causing the stator to turn via its pads kept in permanent contact against the friction lining of the rotor generates a centrifugal force applied to the pads. This centrifugal force is added to the spring force to obtain driving at the same speed between the stator and rotor and is cancelled under the action of accidental blocking of the stator to momentarily neutralize the driving between the rotor and stator by the shoes' sliding on the surface of the friction lining of the rotor. This coupler has a large number of advantages relative to existing systems. In fact, it allows limitation of wear of parts and minimization of heating. This coupler, during the phase of starting the turning of the engine, makes it possible in particular to obtain significant reactivity of the stator and in particular high speed driving to increased rpm of the stator due to the presence of a compression spring that permanently applies a radial force to the pad and tends to keep it in constant contact with the friction lining of the rotor.
So that this starting phase and subsequent operating phases proceed optimally, it is necessary for the friction surface between the pads and the friction lining of the rotor to be of a relatively significant size to avoid any slipping. In the version described in the aforementioned French patent, this surface remains unchanged regardless of the operating phases of the stator. Thus, whether the stator is immobilized due to the presence of an obstacle or not, the friction surface between the pads and rotor remains identical. For this reason, significant heating and faster wear of the pad during the slipping phases corresponding to the phases of deceleration or blockage of the stator can again be observed.
Moreover, all of the above-described devices generate major vibrations because in each of the preceding cases, the shaft bearing the pads and allowing their movement to enable driving of the stator is fixed. The transmission of vibrations through this shaft is therefore damped very little. As a result, the user of a machine equipped with such a device is exposed to major vibrations that can entail muscle-skeletal problems in the arm-hand system or at the level of the spinal column.
Therefore, approaches are being sought at present that would allow the coupler, at the level of the starting phase, to have the same advantages as those mentioned above, while reducing the problems of heating during slipping phases and vibration problems during operation.